I would advise you not to do it, as a consistent writing style is much more appreciated by readers. That said, if you right click on an in-text citation, you should have an option 'Edit Citation', there you can suppress the author. You would then manually
have to type the name in front of the brackets.

There is no way to offer two different fully functional formatting styles for in-text citations in the same document by default in Word. If you are adventurous and have some xslt skills, you could abuse one of the field switches and create your own implementation
supporting just this.